Metal wood club with improved hitting face

ABSTRACT

A hitting face of a golf club head having improved flexural stiffness properties. In one embodiment, the hitting face is made from multiple materials. The main portion of the hitting face is a plate-like face made from a first material having a first density. A dense insert made from a second material having a second density that is greater than the first density is attached directly or indirectly to the plate-like face at or near the geometric center thereof. The dense insert increases the flexural stiffness of in a central zone of the hitting face so that a golf club head that has a larger zone of substantially uniform high initial ball speed. In another embodiment, the hitting face includes an insert that includes main plate and at least one wing extending therefrom. The insert is welded to the golf club head so that the main plate does not deflect separately from the remainder of the hitting face. The geometry of the insert controls the stiffness in the axial directions.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. application Ser. No.11/780,886 filed on Jul. 20, 2007, which is a divisional of U.S.application Ser. No. 10/911,422 filed on Aug. 4, 2004 and issued as U.S.Pat. No. 7,261,643 on Aug. 28, 2007, which is continuation-in-part ofU.S. application Ser. No. 10/428,061 filed on May 1, 2003 and issued asU.S. Pat. No. 7,029,403 on Apr. 18, 2006, which is acontinuation-in-part of U.S. application Ser. No. 09/551,771 filed onApr. 18, 2000 and issued as U.S. Pat. No. 6,605,007 on Aug. 12, 2003,the disclosures of which are incorporated herein by reference in theirentireties.

FIELD OF THE INVENTION

The present invention relates to an improved golf club head. Moreparticularly, the present invention relates to a golf club head with animproved striking face having a relatively large zone of high initialball velocity.

BACKGROUND

The complexities of golf club design are well known. The specificationsfor each component of the club (i.e., the club head, shaft, grip, andsubcomponents thereof) directly impact the performance of the club.Thus, by varying the design specifications, a golf club can be tailoredto have specific performance characteristics.

The design of club heads has long been studied. Among the more prominentconsiderations in club head design are loft, lie, face angle, horizontalface bulge, vertical face roll, center of gravity, inertia, materialselection, and overall head weight. While this basic set of criteria isgenerally the focus of golf club engineering, several other designaspects must also be addressed. The interior design of the club head maybe tailored to achieve particular characteristics, such as the inclusionof hosel or shaft attachment means, perimeter weights on the club head,and fillers within hollow club heads.

Golf club heads must also be strong to withstand the repeated impactsthat occur during collisions between the golf club and the golf ball.The loading that occurs during this transient event can create a peakforce of over 2,000 lbs. Thus, a major challenge is designing the clubface and body to resist permanent deformation or failure by materialyield or fracture. Conventional hollow metal wood drivers made fromtitanium typically have a uniform face thickness exceeding 2.5 mm toensure structural integrity of the club head.

Players generally seek a metal wood driver and golf ball combinationthat delivers maximum distance and landing accuracy. The distance a balltravels after impact is dictated by the magnitude and direction of theball's translational velocity and the ball's rotational velocity orspin. Environmental conditions, including atmospheric pressure,humidity, temperature, and wind speed, further influence the ball'sflight. However, these environmental effects are beyond the control ofthe golf equipment manufacturer. Golf ball landing accuracy is driven bya number of factors as well. Some of these factors are attributed toclub head design, such as center of gravity and club face flexibility.

The United States Golf Association (USGA), the governing body for therules of golf in the United States, has specifications for theperformance of golf balls. These performance specifications dictate thesize and weight of a conforming golf ball. One USGA rule limits the golfball's initial velocity after a prescribed impact to 250 feet per second+2% (or 255 feet per second maximum initial velocity). To achievegreater golf ball travel distance, ball velocity after impact and thecoefficient of restitution of the ball-club impact must be maximizedwhile remaining within this rule.

Generally, golf ball travel distance is a function of the total kineticenergy imparted to the ball during impact with the club head, neglectingenvironmental effects. During impact, kinetic energy is transferred fromthe club and stored as elastic strain energy in the club head and asviscoelastic strain energy in the ball. After impact, the stored energyin the ball and in the club is transformed back into kinetic energy inthe form of translational and rotational velocity of the ball, as wellas the club. Since the collision is not perfectly elastic, a portion ofenergy is dissipated in club head vibration and in viscoelasticrelaxation of the ball. Viscoelastic relaxation is a material propertyof the polymeric materials used in all manufactured golf balls.

Viscoelastic relaxation of the ball is a parasitic energy source, whichis dependent upon the rate of deformation. To minimize this effect, therate of deformation must be reduced. This may be accomplished byallowing more club face deformation during impact. Since metallicdeformation may be purely elastic, the strain energy stored in the clubface is returned to the ball after impact thereby increasing the ball'soutbound velocity after impact.

A variety of techniques may be utilized to vary the deformation of theclub face, including uniform face thinning, thinned faces with ribbedstiffeners and varying thickness, among others. These designs shouldhave sufficient structural integrity to withstand repeated impactswithout permanently deforming the club face. In general, conventionalclub heads also exhibit wide variations in initial ball speed afterimpact, depending on the impact location on the face of the club. Hence,there remains a need in the art for a club head that has a larger “sweetzone” or zone of substantially uniform high initial ball speed.

SUMMARY OF THE INVENTION

The present invention relates to a golf club head adapted for attachmentto a shaft. An embodiment of the present invention is a golf club headthat includes a hitting face made from multiple materials, wherein thefirst material forms a central zone of the hitting face. The centralzone has a first flexural stiffness. The second material forms anintermediate zone of the hitting face concentric with the central zone.The intermediate zone has a second flexural stiffness that is lower thanthe first flexural stiffness.

Another embodiment of the present invention is a golf club head thatincludes a crown forming an upper surface of the golf club head, a soleforming a lower surface of the golf club head, and a hitting facedisposed between the crown and the sole, wherein the hitting faceincludes a face insert welded around the perimeter thereof to the golfclub head. The face insert includes a main plate and at least one wingextending therefrom.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred features of the present invention are disclosed in theaccompanying drawings, wherein similar reference characters denotesimilar elements throughout the several views, and wherein:

FIG. 1 is a front view of a striking face of the golf club headdisclosed in the parent patent application; FIGS. 1 a and 1 b arecross-sectional views of the striking face of FIG. 1 taken along lines1A-1A and 1B-1B, respectively; FIG. 1 c is an alternate embodiment fromthe priority patent;

FIG. 2 is a front, exploded view of an alternate embodiment of theparent patent invention;

FIG. 3 is a front plan view of an embodiment of a hitting face of thepresent invention;

FIG. 3A is a cross-sectional view of the hitting face of FIG. 3 takenalong line 3A-3A;

FIG. 3B is an exploded cross-sectional view of the hitting face of FIG.3;

FIG. 4 is a cross-sectional view of an alternate embodiment of a hittingface of the present invention;

FIG. 5 is a cross-sectional view of another alternate embodiment of ahitting face of the present invention;

FIG. 6 is a cross-sectional view of another alternate embodiment of ahitting face of the present invention;

FIG. 7 is a cross-sectional view of another alternate embodiment of ahitting face of the present invention;

FIG. 8 is a cross-sectional view of another alternate embodiment of ahitting face of the present invention;

FIG. 8A is an exploded cross-sectional view of the hitting face of FIG.8;

FIG. 9 is a front exploded view of an alternate embodiment of a clubhead;

FIG. 10 is a perspective view of another alternate embodiment of a clubhead of the present invention;

FIG. 11 is a perspective view of another alternate embodiment of a clubhead of the present invention;

FIG. 12 a is a top perspective view of another alternate embodiment of aclub head of the present invention;

FIG. 12 b is a bottom perspective view of the club head shown in FIG. 12a;

FIG. 13 a is a top perspective view of another alternate embodiment of aclub head of the present invention;

FIG. 13 b is a bottom perspective view of the club head shown in FIG. 13a;

FIG. 14 is a graph of inertance versus frequency for a conventional clubhead; and

FIG. 15 is a graph of inertance versus frequency for the inventive clubhead discussed in priority case.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Priority U.S. Pat. No. 6,605,007, which has been incorporated herein inits entirety, discloses an improved golf club that also produces arelatively large “sweet zone” or zone of substantially uniform highinitial velocity or high coefficient of restitution (COR).

COR or coefficient of restitution is a measure of collision efficiency.COR is the ratio of the velocity of separation to the velocity ofapproach. In this model, therefore, COR was determined using thefollowing formula:

(v_(club-post)−v_(ball-post))/(v_(ball-pre)−v_(club-pre))

where,

-   -   v_(club-post) represents the velocity of the club after impact;    -   v_(ball-post) represents the velocity of the ball after impact;    -   v_(club-pre) represents the velocity of the club before impact        (a value of zero for USGA COR conditions); and    -   v_(ball-pre) represents the velocity of the ball before impact.

COR, in general, depends on the shape and material properties of thecolliding bodies. A perfectly elastic impact has a COR of one (1.0),indicating that no energy is lost, while a perfectly inelastic orperfectly plastic impact has a COR of zero (0.0), indicating that thecolliding bodies did not separate after impact resulting in a maximumloss of energy. Consequently, high COR values are indicative of greaterball velocity and distance.

As shown in FIG. 1, 1 a and 1 b, the accuracy of the club and the club'slarge zone of uniform high initial velocity are produced by hitting face2, having central zone 4, a surrounding intermediate zone 6, and anoptional perimeter zone 8. Preferably, the area of central zone 4comprises about 15% to about 60% of the total area of the hitting face2, and more preferably about 20% to about 50%.

Central zone 4 is comparatively rigid and intermediate zone 6 isrelatively flexible so that upon ball impact, intermediate zone 6 offace 2 deforms to provide high ball velocity, while central zone 4 issubstantially undeformed so that the ball flies on-target. Thus, uponball impact the deformation of intermediate zone 6 allows central zone 4to move into and out of a club head 10 as a unit. Surroundingintermediate zone 6 may be located adjacent to central zone 4, andoptional perimeter zone 8 may be located adjacent to intermediate zone6. As a result, the head exhibits a coefficient of restitution greaterthan about 0.81.

The above is accomplished by providing central zone 4 with a firstflexural stiffness and intermediate zone 6 with a second flexuralstiffness. Flexural stiffness (FS) is defined as each portion's averageelastic modulus (E) times each portion's average thickness (t) cubed or(FS =Et³). The calculation of averages of modulus and thickness is fullydisclosed in the parent application and in the '007 patent, which havealready been incorporated by reference in their entireties. Thedetermination of FS when the thickness varies or when the material isanisotropic is also fully discussed in the parent patent application andin the '007 patent.

Since the flexural stiffness is a function of material and thickness,the following techniques can be used to achieve the substantialdifference between the flexural stiffness of central zone 4 andintermediate zone 6: 1) different materials can be used for eachportion, 2) different thicknesses can be used for each portion, or 3)different materials and thickness can be used for each portion. Forexample, in a preferred embodiment, the thickness of the central zone isgreater than the thickness of the intermediate zone and the material forboth portions is the same.

In club head 10, the above flexural stiffness relationships can beachieved by selecting a certain material with a particular elasticmodulus and varying the thickness of the zones. In another embodiment,the flexural stiffness relationships can be achieved by varying thematerials of the zones with respect to one another so that the zoneshave different elastic moduli and the thickness is changed accordingly.Thus, the thickness of the zones can be the same or different dependingon the elastic modulus of the material of each zone. It is also possibleto obtain the required flexural stiffness ratio through the use ofstructural ribs, reinforcing plates, and thickness parameters. Theparent case application and the grandparent '007 patent describe indetail the preferred ranges of ratios of flexural stiffness betweencentral zone 4 and intermediate zone 6.

Further, as discussed in the '007 patent, two or more differenthomogeneous materials may be used to form hitting face 2. For example,central zone 4 may be of generally uniform thickness and made from astainless steel having a Young's Modulus of 30.0×10⁶ lbs/in². Theadjacent intermediate zone 6 has a continuously tapering thickness fromthe pace perimeter toward central zone 4. The thickness of intermediatezone 6 is defined to change linearly. Intermediate zone 6 is made from atitanium alloy having a Young's Modulus of 16.5×10⁶ lbs/in².Alternatively, as shown in FIG. 1 c, which corresponds to FIG. 10 fromthe '007 patent, central zone 4 may include ribs 4 a made of stainlesssteel having a Young's Modulus of 3.0×10⁶ lbs/in² with a titanium alloyhaving a Young's Modulus of 1 6.5×10⁶ lbs/in in the interstitial spaces4 b. Intermediate zone 6 is made from the same titanium alloy. Theflexural stiffness ratio between central zone 4 and intermediate zone 6is calculated in detail in the '007 patent.

Optional perimeter zone 8 preferably increases in thickness compared tointermediate zone 6 to increase the flexural stiffness thereof.Alternatively, optional perimeter zone 8 may increase in flexuralstiffness compared to intermediate zone by forming perimeter zone 8 outof a different material than that of intermediate zone 6. For example,perimeter zone 8 may be made of the same material as central zone 4.Alternatively, perimeter zone 8 may be made of an entirely differentmaterial than that of central zone 4 or intermediate zone 6. Perimeterzone 8 would then be attached to intermediate zone 6, such as bywelding.

Referring now to FIG. 2, which corresponds to FIG. 8 from the parentcase, hitting face 2 may comprise a face insert 42, which is welded ontoa cavity defined on the face. Hitting face 2 may comprise a face insert42 and face support 30. In this embodiment, hitting face 2 is delineatedfrom crown 14, toe 18, sole 22 and heel 32 by parting line 46. Centralzone 4 is preferably disposed on the inner-cavity-facing surface of faceinsert 42, and, as shown, has a generally elliptical shape. Theelliptical central zone 4 is fully disclosed in the parent patentapplication. Central zone 4 is preferably aligned in the direction ofthe low toe to high heel, so that a high COR zone can be established inthe direction of high tow to low heel. This high COR zone advantageouslycoincides with the typical impact patterns created by golfers.

As defined in the parent case, the term “ellipse” or “elliptical” refersto non-circular shapes that have discernable major axis and minor axis,and include, but are not limited to, any quadrilateral shapes,geometrical ellipses, quadrilateral shapes with one or more roundedcorner(s) and unsymmetrical elliptical shapes. The “major axis” isdefined as the axis coinciding with the longest length that can be drawnthrough the non-circular shapes without intersecting the perimeter ofthe shapes at more than two locations, i.e., at the start and end pointsof said length. The “minor axis” is orthogonal to the major axis at ornear its midpoint. As used herein, the term “concentric” refers toshapes that substantially encircle or surround other shapes.

Intermediate zone 6, designated as 6 ₁ and 6 ₂, can be disposedpartially on face insert 42 and partially on face support 30. Atransition zone 7 having variable thickness is disposed between centralzone 4 and intermediate zone 6. Preferably, the thickness of centralzone 4 is reduced to the lesser thickness of intermediate zone 6 withintransition zone 7. This reduces any local stress-strain caused byimpacts with golf balls due to abrupt changes in thickness. Face support30 defines hole 48, which is bordered by rim 49. Face insert 42 can beattached to face support 30 by welding at or around rim 49.

Preferably, face insert 42 is made by milling or stamping and forming.In the manufacturing process, a malleable metal suitable for use as ahitting face, such as titanium, titanium alloy, carbon steel, stainlesssteel, beryllium copper, and other forgeable metals, is heated and thenhammered into the desired shape of the face cup. Examples of someappropriate metals include but are not limited to titanium 6-4 alloy,titanium 15-3-3-3 alloy, titanium 20-4-1 alloy, and DAT 55 and DAT 55G,titanium alloys available from Diado Steel of Tokyo, Japan.

The preferred forging process is die or billet forging, in which apre-measured rod of forgeable metal is heated and placed between a die,which contains the desired shape of face insert 42, and a hammer. Theheated metal is then hammered into the desired shape. An advantage offorging face insert 42 is that the thickness of the face can be as thinas about 0.060 inch (or about 1.5 mm) around the perimeter or edgethereof.

Referring now to FIGS. 3-8, alternate embodiments of hitting face insert42 are shown. In these embodiments, the flexural stiffness of centralzone 4 is higher than the flexural stiffness of intermediate area 6 dueto a dense insert 52 made of a material of greater density than that ofthe material forming the remainder of face insert 42. A cross-sectionalview of a preferred embodiment of the present invention is shown in FIG.3A, wherein face insert 42 includes a plate-like face 50 and an insert52.

Plate-like face 50 is preferably elliptical in shape with a slightlycurved profile, although any shape may be used, such as polygonal,circular or irregular.

The size of plate-like face 50 depends upon the overall size of golfclub head 10. However, in a preferred embodiment, plate-like face 50measures between 80 and 100 mm along the long axis of the ellipse andbetween 35 and 60 mm along the short axis of the ellipse. Morepreferably, plate-like face 50 measures 90 mm along the long axis of theellipse and 50 mm along the short axis. Plate-like face 50 may be ofuniform or non-uniform thickness 53. In one embodiment, thickness 53ranges from 2-5 mm. Preferably, thickness 53 is 2.7 mm graduallytapering to a maximum thickness of 4.5 mm.

Plate-like face 50 preferably includes a cavity 51, shown in theexploded view of FIG. 3B, formed on the surface 55 that faces the innercavity of golf club head 10. Further, in the vicinity of cavity 51,plate-like face 50 preferably increases in thickness, so as to combinethe effects of a thickened central zone as described above with theeffects of the denser material of dense insert 52. In this embodiment,cavity 51 is circular in shape, although the shape of cavity 51 ispreferably chosen to correspond to the cross-sectional shape of denseinsert 52. Although cavity 51 may be made of any size sufficient toaccommodate dense insert 52, in one embodiment, cavity 51 has aninterior width of approximately 14 mm and a depth of approximately 2 mm.

As discussed above, plate-like face 50 is preferably forged, althoughstamping and casting are also suitable manufacturing techniques.Plate-like face 50 may be made of any material discussed herein that issuitable for forming hitting face 2, such as titanium, titanium alloy,carbon steel, stainless steel, beryllium copper. The more preferredmetal is titanium 6-4 alloy, as described above.

Dense insert 52 is shown as being a conical frusta that is relativelysmall in cross-sectional surface area compared to plate-like face 50.Dense insert 52 may take on any shape that is convenient formanufacturing, for example a cylinder or a circular, elliptical orquadrilateral disk. Dense insert 52 is made of a material of greaterdensity than that of plate-like face 50, preferably tungsten orstainless steel, although any material of greater density thanplate-like face 50 is appropriate for use in the present invention,including copper, nickel, and bronze. Dense insert 52 may be milled,stamped from sheet metal, forged, die cut, cast, or made using anytechnique known in the art.

Dense insert 52 is preferably small compared to the size of plate-likeface 50. In the preferred embodiment, dense insert 52 is approximately10 mm in diameter at its widest point and approximately 7 mm in height.As such, dense insert 52 protrudes from surface 55 of plate-like face50, as dense insert 52 is of a greater height than the depth of cavity51. The size of dense insert 52 may be varied so as to control theeffective size of central zone 4.

Dense insert 52 may be directly or indirectly affixed to plate-like face50. In the preferred embodiment, dense insert 52 is contained within acap 56 made of the same material as that used to make plate-like face 50so that cap 56 may be readily welded to plate-like face 50. Dense insert52 may be affixed to an interior surface of cap 56, adhered to at leastone interior surface of cap 56, or simply rest within cap 56. As shown,cap 56 is a conical frusta having an interior cavity shaped so thatdense insert 52 fits tightly within cap 56. Cap 56 may be made using anymethod known in the art, such as casting, stamping or forging.

As such, dense insert 52 is indirectly fixedly attached to plate-likeface 50, in that dense insert 52 is contained within cap 56 which isjoined to plate-like face 50 by a weld bead 58 so that dense insert 52is not dislodged from its position during the repeated impacts ofhitting face 2 with golf balls. Alternately, at least a portion of thecombination of dense insert 52 and cap 56 may be secured within cavity51 using an adhesive, for example hot melt adhesives, epoxy adhesives,polyurethane adhesives, sealants, thermoset adhesives, UV curingadhesives, silicon adhesives, acrylic and cyanoacrylic adhesives.

Referring to FIG. 4, an alternate embodiment of face insert 42 having adense insert 52 is shown. In this embodiment, dense insert 52 is acircular disk that is adhered directly to the inner cavity-facingsurface 55 of plate-like face 50. Alternatively, dense insert 52 mayalso be welded to the surface of plate-like face 50.

Referring to FIG. 5, another alternate embodiment of face insert 42having a dense insert 52 is shown. In this embodiment, plate-like face50 includes a cavity 51 into which dense insert 52 in the shape of acircular disk in inserted. Dense insert 52 may or may not be affixed tothe surface of cavity 51, such as with an adhesive. A flange portion 54extends over dense insert 52 to hold dense insert 52 within cavity 51,i.e., to prevent dense insert 52 from being ejected from cavity 51during repeated impacts with golf balls. Flange portion 54 may be apiece of material welded to plate-like face 50. Alternatively, flangeportion 54 may be formed during manufacturing of plate-like face 50.Face insert 42 is preferably milled and/or stamped. During themanufacturing process, cavity 51 is formed in a thickened central zoneof plate-like face 50. Cavity 51 is formed to a height that is slightlyhigher than the height of dense insert 52. Dense insert 52 is thenpositioned within cavity 51 and preferably adhered to an inner surfaceof cavity 51. The surface of plate-like face 50 is then forcibly struckor hammered to deform the portion cavity 51 protruding over dense insert52, thereby forming flange portion 54.

Referring to FIG. 6, another alternate embodiment of multiple-materialface insert 42 is shown. This embodiment includes a plate-like face 50similar to the plate-like faces of earlier-described embodiments.However, in this embodiment, plate-like face includes a thin-walledcup-like protrusion 60 extending outward from the inner cavity-facingsurface 55 of plate-like face 50. Cup-like protrusion 60 is shown as afrusta, although it may have any shape, such as a hollow cylinder,three-dimensional polygon, or an irregular shape.

Dense insert 52, similar to the dense inserts described above, is sizedand dimensioned to fit tightly within cup-like protrusion 60. Denseinsert 52 may be affixed to the interior of cup-like protrusion 60using, for example, an adhesive. However, dense insert 52 is held withincup-like protrusion 60 by flange portion 54, similar toearlier-discussed flange portions. In this embodiment, however, if thestamping technique is used to form flange portion 54, the excessmaterial comes from the excess height of cup-like protrusion 60.

Referring to FIG. 7, a cross-sectional view of another alternateembodiment of a face insert 42 of the present invention is shown. Inthis embodiment, plate-like face 50 is similar to the plate-like facedescribed above with respect to the preferred embodiment. In thisembodiment, however, cap 56 is a hollow cylinder having an outerdiameter that is less than the diameter of cavity 51. Dense insert 52 isa cylindrical plug that fits tightly within cap 56, preferably affixedtherewithin.

Cap 56 includes a brim 64 that is sized and dimensioned to fit snuglywithin cavity 51. As such, a small amount of clearance exists betweenthe outer diameter of cap 56 and the edge of cavity 51. Weld bead 58 isformed around the edge of cavity 51 and the edge of brim 64 to attachcap 56 to plate-like face 50. This geometry of cap 56 increases thesurface area to which weld bead 58 may affix, thereby increasing thestrength of the joint. As such, the usable life of hitting face 2increases, as the stronger joint is less likely to suffer failure andeject dense insert 52 into the inner cavity of golf club head 10.

Referring now to FIGS. 8 and 8A, yet another alternate embodiment of aface insert 42 of the present invention is shown. In this embodiment,face insert 42 includes plate-like face 50 and a dense insert 52.However, a void 61 is formed at or near the center of plate-like face 50extending entirely through the thickness thereof. Dense insert 52 ispreferably configured such that at least a portion thereof is fittedinto void 61 while a brim portion 63 thereof rests upon or is affixed toa lip or shelf 66 formed in void 61. A flange portion 54, similar tothose flange portions described above, holds dense insert 52 securely inplace. As such, dense insert 52 is visible from the exterior-facingsurface 65 of plate-like face 50. Although the exterior-facing surfaceof dense insert 52 is shown as being substantially flush with surface65, this need not be the case and a gap may exist between the edges ofvoid 61 such that dense insert 52 is still visible.

EXAMPLE

Inventive Club W is a hollow metal wood club head made generally inaccordance with the embodiment shown in FIG. 7. Club W includes a faceinsert made of a plate of titanium alloy having a tungsten insert weldedto the inner-cavity-facing surface thereof at or near the geometriccenter of the plate. As such, the thickness of Club W varies in that thecentral zone of the face insert is thicker than the perimeter thereof.Club W has a COR measured to be 0.812.

A standard King Cobra® SZ 440 club head is also a hollow metal wood clubhead. The SZ 440 club head has a hitting face having variable thickness.Similar to Club W, the SZ 440 club head is thicker near the geometriccenter of the hitting face and thinner toward the perimeter thereof.However, the thickness variations of the SZ 440 club head hitting faceare manufactured integrally with the hitting face, i.e., the hittingface includes a single plate of material that is machined to remove aportion of the material only around the perimeter of the plate. The SZ440 club head has a COR of 0.814, approximately equal to that of Club W.

Both clubs were tested using the pendulum test, which is the standardtest for club face flexibility or trampoline effect under USGA andinternational rules. This test entails impacting a specific spot golfclub head several times using a small steel pendulum. A characteristictime between the club head and the pendulum is recorded in microseconds(μs), thereby determining the flexibility of the golf club head at thatpoint. In accordance with USGA rules, nine points on the golf club headare so tested. Generally, the longer the characteristic time, thegreater the flexibility of the golf club head.

As shown in Table 1, the characteristic time of the pendulum with Club Wis greater than that of the SZ 440 club face at all tested points. Assuch, the flexibility of Club W is greater than that of the SZ 440 clubface, even though the COR value is approximately the same for both clubheads.

TABLE 1 Nine Point Pendulum Test Results SZ 440, Club W PEN PEN PEN PENPEN PEN PEN PEN PEN High High High Low Low Low Club Model Center ToeHeel Center Toe Heel Center Toe Heel Comparative 235 238 235 229 244 240227 226 232 SZ 440 Inventive Club 251 269 250 251 266 263 268 255 235 W

In accordance with another aspect of the present invention, thethickness of intermediate zone 6 or optional perimeter portion 8 onhitting face 2 can be thinly manufactured by removing the weld linesfrom the hitting face to the crown and sole of the club head. Analternate method for improving the performance of hitting face 2 is toremove weld lines and joints of face insert 42 to another surface ofclub head 10. As is known in the art, a weld line or joint is an area ofdiscontinuity, where even if two pieces of the same material are joined,the structural properties of the pieces in the vicinity of the joint arealtered. Removing weld lines to the crown or the sole of a club headallows the thickness of the hitting face to be controlled more preciselyand allows for a thinner overall hitting face. The joints can also beused to alter the properties of the hitting face. In accordance withthis aspect of the invention, the face insert may include one or moreside walls, wherein the side walls may form part of the crown and/orpart of the sole.

Referring to FIG. 9, which corresponds to FIG. 9 from the parent case,face insert 42 comprises central zone 4, transition zone 7, a portion ofintermediate zone 6, partial crown portion 54 and partial sole portion56. Club head 10 correspondingly defines cavity 58 sized and dimensionedto receive face insert 42. Face insert 42 is preferably welded to clubhead 10. Face insert 42 together with face support 30 forms hitting face2. Similar to the embodiment illustrated in FIG. 2, intermediate zone 6,designated as 6 ₁ and 6 ₂, can be disposed partially on face insert 42and partially on face support 30.

Referring now to FIG. 10, another embodiment according to the presentinvention is shown. In this embodiment, central zone 4 of hitting face 2is formed of a face insert 42. Face insert 42 is preferably welded toclub head 10 along weld line 20. Face insert 42 includes a polygonal orelliptical main plate 34 and a sidewall or wing 70 that extends into andforms a part of crown 14. As such, an upper portion 71 of weld line 20is removed to crown 14. As the stress line created by weld line 20 isremoved from hitting face 2, the probability of failure along upperportion 21 due to repeated impact with golf balls is reduced.

Face insert 42 is preferably made from the same material as the rest ofclub head 10, such as titanium, a titanium alloy, steel, or any othermaterial suitable for use as a club head. Face insert 42 is preferablythe same thickness as the rest of club head 10, although face insert 42may be made thicker or thinner in order to affect the flexural stiffnessthereof.

The size and shape of face insert 42 may vary. As stated above,preferably, face insert 42 is a modified oval U-cup or L-cup, but it mayalso be other shapes, such as rectangular, elliptical or circular. Faceinsert 42 preferably forms nearly the entire surface area of hittingface 2. However, face insert 42 may form a much smaller portion ofhitting face. Also, wing 70 may extend into and form a part of sole 22,as shown in FIG. 11, by simply inverting the configuration of faceinsert 42. In this case, the affected weld line is lower weld line 73.

The material properties of face insert 42 can also be affected by themethod chosen to form face insert 42. For example, face insert 42 ispreferably stamped from sheet metal after the metal has been cold rolledor cold worked in order to align the crystal grains of the metal.Stamping metal in this fashion produces a stronger hitting face thanother manufacturing techniques. Further, face insert 42 is thenpositioned within hitting face 2 so that the grain flow pattern of faceinsert 42 runs in a sole-to-crown direction. Alternatively, the grainflow pattern of face insert 42 may run in a heel-to-toe direction or ina diagonal direction. Other methods known in the art may also be used tomanufacture face insert 42, such as forging and casting.

FIGS. 12 a and 12 b show another embodiment of club head 10 similar tothe embodiment shown in FIG. 10. In this embodiment, face insert 42includes a main plate 34, an upper sidewall or wing 70 that extends intoand forms part of crown 14 as well as a lower wing 72 that extends intoand forms part of sole 22. As such, upper weld line 71 and lower weldline 73 are removed to crown 14 and sole 22, respectively, so as toreduce the potential for failure thereof. All other aspects of faceinsert 42 are as described above with respect to FIG. 10.

FIGS. 13 a and 13 b show yet another embodiment of club head 10 similarto the embodiment shown in FIG. 10. In this embodiment, face insert 42includes an upper sidewall or wing 70 that extends into and forms partof crown 14, a lower sidewall or wing 72 that extends into and formspart of sole 22, a heel extension 74, and a toe extension 75. Upper wing70 and lower wing 72 are as described above with respect to FIGS. 10, 12a, and 12 b. Heel extension 74 and toe extension 75 are extensions ofthe main plate of face insert 42 along the horizontal axis 76 thereof ator near the center of the vertical axis 78 thereof. This alteration ofthe geometry of face insert increases the deflection capabilities offace insert 42 along horizontal axis 76 while vertical axis 78 has adifferent, lesser deflection capability.

Face insert 42 is preferably of a size and general shape as describedabove with respect to the embodiment shown in FIGS. 10, 12 a and 12 b,i.e., a polygonal or elliptical main plate that forms much of thesurface area of hitting face 2. Upper wing 70 and lower wing 73 arepreferably generally elliptical or polygonal, although other shapes arecontemplated by the present invention. Similarly, heel extension 74 andtoe extension 75 are preferably semi-elliptical in shape, although othershapes such as semi-circular are contemplated by the present invention.As such, the preferred geometry of face insert 42 is a central ovalhaving a long axis along horizontal axis 76 of hitting face 2 andgenerally rectangular extensions stretching along vertical axis 78 ofhitting face 2. Further, one of heel extension 74 and toe extension 75may be eliminated. Also, one or both of upper wing 70 and lower wing 73may be eliminated. Further, face insert 42 may incorporate a denseinsert as shown in any of the embodiments shown in FIGS. 3-8 forincreased performance effects. Face insert 42 may also contain centralzone 4 and intermediate zone 6, where the flexural stiffness of centralzone 4 is higher then the flexural stiffness of intermediate zone 6, asdescribed above and as described in the parent application and in thegrandparent '007 patent. Additionally, central zone 4 may also include adense insert 52 as described above.

Hitting face 2 is preferably milled or stamped and milled. The body ofclub 10 is preferably cast. The inner cavity of club head 10 may beempty, or alternatively may be filled with foam or other low specificgravity material. It is preferred that the inner cavity has a volumegreater than 250 cubic centimeters, and more preferably greater than 275cubic centimeters, and most preferably 350 cubic centimeters or more.Preferably, the mass of the inventive club head is greater than 150grams but less than 220 grams. Further part and manufacturing detailsand additional test results regarding the COR values of inventive clubheads are discussed in detail in the parent case.

Yet another parameter that reflects the stiffness of a structure isinertance. Generally, inertance is a frequency response. Morespecifically, inertance reflects the stiffness of a structure, in thisinstance the club face, at various frequencies of vibration. The unitsof inertance are acceleration units over force units. A preferred firstresonant frequency for the inventive club face described herein islocated where inertance is maximized. The testing methodology andapparatus for determining inertance are described in further detail inthe parent patent, U.S. Pat. No. 6,605,007, which patent is incorporatedherein in its entirety by reference.

Referring to FIG. 14, a graph of inertance versus frequency for aconventional club head is shown. The conventional club head is aCallaway Great Big Bertha War Bird with an eight degree loft. The point11 at a frequency of 3330 Hertz represents the first primary resonantfrequency which occurs at the first primary maxima inertance for theinertance function I. A maxima which does not represent a primaryresonant natural frequency of the face is also present in FIG. 14 at afrequency of 2572 Hertz, which is designated as point 12. Thesesecondary maxima 12 are characterized by inertance transitions of amagnitude of less than 10 decibels. These secondary maxima may be due tocrown, sole or skirt vibrations that are not acting perpendicular to theplane of the club face. Secondary maxima do not correlate with COR andball velocity, since the vibration response is either small in magnitudeor alternately not coincident with ball response. The COR for theconvention club head tested was measured in accordance with USGA, Rule4-1e Appendix II Revision 2 dated Feb. 8, 1999 and was found to be0.785. The preferred first primary resonant frequency of vibration isdefined by the following relationship:

1/(2*contact duration)<I1<3/(2*contact duration)

The contact duration is the time interval during which the ball is incontact with the club face. The contact duration for a typical driverimpact is about 500 microseconds. Thus, the preferred primary resonantfrequency of vibration for the conventional club head is between about1000 and 3000 Hertz. The closer the COR is to the lower limit, thehigher the COR and thus the higher the rebound ball velocity. Morepreferably, the first primary resonant frequency is less than 2900.

FIG. 15 illustrates the inertance function of the inventive club headdescribed and claimed in priority U.S. Pat. No. 6,605,007 (“the '007club”). The first primary resonant frequency of vibration for the clubhead is at 2632 Hertz, and the COR of the '007 club was measured to be0.824. The COR of the '007 club was measured to be 0.824. The COR of the'007 club is greater than the conventional club of FIG. 14, andtherefore will provide greater ball rebound velocity.

The overall flexural stiffness of a club head and the distribution ofthe flexural stiffness across the face of the club head impact theresonant frequency of a club head. Furthermore, the swing speed willdetermine if the club and/or a golf ball vibrates at the resonantfrequency upon impact. As such, by altering the structural design andproperties of a club head, a club designer may alter the resonantfrequency of the club head to coordinate with the resonant frequency ofa particular golf ball so as to maximize the distance traveled by theball when struck at a certain swing speed. Also, if the club is designedwith a particular golfer in mind, the club can be designed to resonateupon striking a particular golf ball at the golfer's average swingspeed. For example, if the club and the ball resonate at a similarfrequency, if they strike each other so as to produce resonance, thenthe vibrations of both club and ball act to push the ball off of theclub face faster. Preferably, the resonance frequency of the club is0-20% greater than the resonant frequency of the ball. More preferably,the resonance frequency of the club is 0-10% greater than the resonantfrequency of the ball.

While various descriptions of the present invention are described above,it should be understood that the various features of each embodimentcould be used alone or in any combination thereof. Therefore, thisinvention is not to be limited to only the specifically preferredembodiments depicted herein. Further, it should be understood thatvariations and modifications within the spirit and scope of theinvention might occur to those skilled in the art to which the inventionpertains. For example, the face and/or individual zones can havethickness variations in a step-wise or continuous fashion. Othermodifications include a perimeter zone that has a thickness that isgreater than or less than the adjacent, intermediate zone. In addition,the shapes of the central, intermediate, and perimeter zones are notlimited to those disclosed herein. Accordingly, all expedientmodifications readily attainable by one versed in the art from thedisclosure set forth herein that are within the scope and spirit of thepresent invention are to be included as further embodiments of thepresent invention. The scope of the present invention is accordinglydefined as set forth in the appended claims.

1. A golf club head comprising: a hitting face comprising a central zoneformed in part of a first material, wherein the central zone has a firstflexural stiffness; and an intermediate zone concentric with the centralzone, wherein the intermediate zone is formed from a second materialthat is different from the first material, wherein the intermediate zonehas a second flexural stiffness, and wherein the first flexuralstiffness is higher than the second flexural stiffness such that on ballimpact, deformation of the intermediate zone allows the central zone tomove into and out of the club as a unit and the club exhibits a primarynatural frequency of less than 2900 Hertz wherein the second materialforms a plate-like face having a geometric center and the first materialforms an insert fixedly attached to the second material at or near thegeometric center.
 2. The golf club head of claim 1, wherein the centralzone comprises about 15% to 60% of the hitting face and being formed inpart of a first material disposed on an inner surface of the hittingface.
 3. The golf club head of claim 1, wherein the second materialforms a plate-like face having a geometric center and the first materialforms an insert fixedly attached to the second material at or near thegeometric center.
 4. The golf club head of claim 3, wherein theplate-like face is configured to receive at least a portion of the firstmaterial at or near the geometric center.
 5. The golf club head of claim4, wherein the plate-like face includes a void formed there through ator near the geometric center configured to receive at least a portion ofthe first material.
 6. The golf club head of claim 4, wherein theplate-like face includes a hollow protrusion formed at or near thegeometric center configured to receive at least a portion of the firstmaterial.
 7. The golf club head of claim 6, wherein the protrusionincludes an overhang formed around a perimeter of the protrusion,wherein the overhang is configured to hold at least a portion of thesecond material within the protrusion.
 8. The golf club head of claim 3,further comprising a hollow cap formed of the second material, whereinthe first material forms a plug that is inserted into the hollow cap andthe cap is fixedly attached to the plate-like face.
 9. The golf clubhead of claim 8, wherein the hollow cap is welded to the plate-likeface.
 10. The golf club head of claim 8, wherein the hollow cap isaffixed to the plate-like face using an adhesive.
 11. The golf club headof claim 8, wherein the plug is affixed to an interior surface of thehollow cap.